pronephros

1. The definitive excretory organ of primitive fishes. SYN: head kidney. 2. In the embryos of higher vertebrates, a vestigial structure consisting of a series of tortuous tubules emptying into the cloaca by way of the primary nephric duct; in the human embryo, the p. is a very rudimentary and temporary structure, followed by the mesonephros and still later by the metanephros. SYN: forekidney, primordial kidney. [pro- + G. nephros, kidney]

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pro·neph·ros (')prō-'nef-rəs, -.räs n, pl -neph·roi -.rȯi either member of the first and most anterior pair of the three paired vertebrate renal organs that functions in the adults of amphioxus and some lampreys, functions temporarily in larval fishes and amphibians, and is present but nonfunctional in embryos of reptiles, birds, and mammals compare MESONEPHROS, METANEPHROS

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n.

the first kidney tissue that develops in the embryo. It is not functional and soon disappears. Compare mesonephros, metanephros.

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pro·neph·ros (pro-nefґros) pl. pronephґroi [pro- + Gr. nephros kidney] 1. a vestigial excretory structure that develops in the human embryo at four weeks, before the mesonephros. Although nonfunctional, its duct is later used by the mesonephros, which arises caudal to it. 2. the definitive excretory organ of primitive fishes.